For low levels of aberration, the RMS wavefront error is not a good predictor of visual acuity. Clinically, it is important to define how aberrations interact to optimize visual performance. New metrics of optical/neural performance that correlate better with clinical measures of visual performance need to be adopted or developed, as well as new clinically viable measures of visual performance that are sensitive to subtle changes in optical performance.

Wavefront-guided refractive surgery and custom optical corrections have reduced the residual root mean squared (RMS) wavefront error in the eye to relatively low levels (typically on the order of 0.25 microm or less over a 6-mm pupil, a dioptric equivalent of 0.19 D). It has been shown that experimental variation of the distribution of 0.25 microm of wavefront error across the pupil can cause variation in visual acuity of two lines on a standard logMAR acuity chart. This result demonstrates the need for single-value metrics other than RMS wavefront error to quantify the effects of low levels of aberration on acuity. In this work, we present the correlation of 31 single-value metrics of optical quality to high-contrast visual acuity for 34 conditions where the RMS wavefront error was equal to 0.25 microm over a 6-mm pupil. The best metric, called the visual Strehl ratio, accounts for 81% of the variance in high-contrast logMAR acuity.

Wave aberrations were measured with a Shack-Hartmann wavefront sensor (SHWS) in the right eye of a large young adult population when accommodative demands of 0, 3, and 6 D were presented to the tested eye through a Badal system. Three SHWS images were recorded at each accommodative demand and wave aberrations were computed over a 5-mm pupil (through 6th order Zernike polynomials). The accommodative response was calculated from the Zernike defocus over the central 3-mm diameter zone. Among all individual Zernike terms, spherical aberration showed the greatest change with accommodation. The change of spherical aberration was always negative, and was proportional to the change in accommodative response. Coma and astigmatism also changed with accommodation, but the direction of the change was variable. Despite the large inter-subject variability, the population average of the root mean square for all aberrations (excluding defocus) remained constant for accommodative levels up to 3.0 D. Even though aberrations change with accommodation, the magnitude of the aberration change remains less than the magnitude of the uncorrected aberrations, even at high accommodative levels. Therefore, a typical eye will benefit over the entire accommodative range (0-6 D) if aberrations are corrected for distance viewing.

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Significance.-Visual performance with wavefront-guided (WFG) contact lenses has only been reported immediately after manufacture without time for habituation, and comparison has only been made with clinically unrefined predicate conventional lenses. We present comparisons of habitual corrections, best conventional scleral lenses, and WFG scleral lenses after habituation to all corrections. Purpose.-To compare, in a cross-over design, optical and visual performance of eyes with corneal ectasias wearing dispensed best conventional scleral lens corrections and dispensed individualized WFG scleral lens corrections. Methods.-Ten subjects (20 eyes) participated in a randomized cross-over study where best conventional scleral lenses and WFG scleral lenses (customized through the 5th radial order) were worn for eight weeks each. These corrections, as well as each subject's habitual correction and normative data for normal eyes, were compared using (1) residual higher-order aberrations (HORMS), (2) visual acuity (VA), (3) letter contrast sensitivity (CS), and (4) visual image quality (logVSX). Correlations were performed between Pentacam biometric measures and gains provided by WFG lenses. Results.-Mean HORMS reduced 48% from habitual to conventional, and 43% from conventional to WFG. Mean logMAR VA improved from habitual (+0.12) to conventional (−0.03

Purpose-To examine if custom wavefront-guided soft contact lenses provide visual and optical performance equivalent to habitual gas permeable (GP) corrections in three keratoconus subjects.Methods-Custom wavefront-guided soft contact lenses were produced and evaluated at the Visual Optics Institute, College of Optometry, University of Houston for three habitual GP-wearing keratoconus subjects. Photopic high and mesopic low contrast logMAR visual acuity and residual 2nd-10th order optical aberrations experienced with these custom soft lenses were recorded and compared to the subjects' habitual GP correction.Results-All three subjects wearing custom soft lenses reached the established exit criterion of photopic high contrast logMAR VA equal to or better than values recorded with their habitual GP lens. High contrast logMAR VA for GP and custom soft lens correction was 0.01±0.05 and 0.00 ±0.02 for KC1, 0.20±0.02 and 0.14±0.02 for KC2 and 0.04±0.09 and −0.05±0.05 for KC3 respectively. Additionally, KC2 reached the exit criterion of high order aberration levels equal to or less than values with their habitual GP lens (GP lens: 0.394 ± 0.024μm, custom lens: 0.381 ± 0.074μm).Conclusions-Custom wavefront-guided soft contact lenses have been demonstrated to provide equivalent photopic high contrast logMAR VA to that achieved with habitual GP correction in three keratoconus subjects. Future emphasis will be placed on surpassing habitual GP performance and reaching a normal age-matched criterion for both visual acuity and aberration measures. Achieving these goals may require a more thorough understanding of the relationship between visual performance and residual aberration experienced during custom lens wear through the use of image quality metrics predictive of visual performance. Keywordskeratoconus; Zernike; wavefront; wavefront-guided; soft contact lens; rigid contact lens; aberration Elevated levels of both lower and higher order aberrations present in the eye disease keratoconus make it difficult for subjects to achieve excellent optical and visual performance with traditional soft contact lenses or spectacles. Consequently, rigid contact lenses have become the current gold standard for the correction of keratoconus, with approximately 65% of keratoconus subjects being fitted with some form of rigid lens correction in both eyes. 1 Rigid lenses reduce unwanted aberrations where conventional soft lenses and spectacles fail due to the ability of the rigid lens to maintain its shape during wear. This results in the formation of a tear lens between the aberrated cornea and rigid lens which masks a portion of the aberration present in these highly aberrated eyes. However, prescribing a rigid lens may not decrease higher order aberration to normal levels, and the elevated levels of residual aberration may continue to have a negative impact on visual performance. 2-4Simulation work in the area of customization has demonstrated that customized correction of lower and higher order aberrations in the keratoconic eye w...

Purpose To examine the performance of state-of-the-art wavefront-guided scleral contact lenses (wfgSCLs) on a sample of keratoconic eyes, with emphasis on performance quantified with visual quality metrics; and to provide a detailed discussion of the process used to design, manufacture and evaluate wfgSCLs. Methods Fourteen eyes of 7 subjects with keratoconus were enrolled and a wfgSCL was designed for each eye. High-contrast visual acuity and visual quality metrics were used to assess the on-eye performance of the lenses. Results The wfgSCL provided statistically lower levels of both lower-order RMS (p < 0.001) and higher-order RMS (p < 0.02) than an intermediate spherical equivalent scleral contact lens. The wfgSCL provided lower levels of lower-order RMS than a normal group of well-corrected observers (p < < 0.001). However, the wfgSCL does not provide less higher-order RMS than the normal group (p = 0.41). Of the 14 eyes studied, 10 successfully reached the exit criteria, achieving residual higher-order root mean square wavefront error (HORMS) less than or within 1 SD of the levels experienced by normal, age-matched subjects. In addition, measures of visual image quality (logVSX, logNS and logLIB) for the 10 eyes were well distributed within the range of values seen in normal eyes. However, visual performance as measured by high contrast acuity did not reach normal, age-matched levels, which is in agreement with prior results associated with the acute application of wavefront correction to KC eyes. Conclusions Wavefront-guided scleral contact lenses are capable of optically compensating for the deleterious effects of higher-order aberration concomitant with the disease, and can provide visual image quality equivalent to that seen in normal eyes. Longer duration studies are needed to assess whether the visual system of the highly aberrated eye wearing a wfgSCL is capable of producing visual performance levels typical of the normal population.